@Chris *********
Okay so if it's a single re-entry permit and you haven't used it (by exiting/re-entering the country on it) you can do your trip no issue and get stamped back in on your 'retirement stamp'
AND
If after that you wanted to get a NEW re-entry permit you'd do that at the office where you got your year extension (you said you did it at Jomtien so that's where you get a new re-entry permit after you come back from the trip so IF you want to leave again you can without losing your retirement visa)